Ethernet is a family of frame-based computer networking technologies for communication networks. It defines a number of wiring and signaling standards for the physical layer of the Open Systems Interconnect (OSI) networking model as well as common addressing format and a variety of medium access control (MAC) procedures at the lower part of the data link layer (OSI layer 2). Ethernet was initially defined as a local area network (LAN) technology to internet the computers within a small organization in which these host computers were close in proximity to each other. Over the years, Ethernet has become such a popular technology that it became the default data link layer mechanism for data transport. Physical topologies of an Ethernet network may comprise, for example, mesh topology or ring topology.
Ethernet rings enable communication of Ethernet data traffic in various ring topologies including a single-ring topology or a multi-ring topology. Ethernet rings may provide wide-area multipoint connectivity more economically than Ethernet meshes due to their reduced number of links. A network device, such as a switch, in an Ethernet ring is called a ring node. Each ring node is connected to adjacent ring nodes participating in the same Ethernet ring, using two independent links. A ring link is bounded by two adjacent ring nodes, and a port for a ring link is called a ring port.
Based on ITU-T Ethernet ring protection switching (ERPS) specification, loop avoidance in an Ethernet ring is achieved by guaranteeing that, at any given time, traffic may flow on all but one of the ring links. This particular link is called the ring protection link (RPL), and under normal conditions this ring protection link is blocked, that is, it is not used for service traffic. One designated ring node, called the RPL owner node, is responsible for blocking traffic at one end of the RPL link. Under an Ethernet ring failure condition, the RPL owner node is responsible for unblocking its end of the RPL link, unless the RPL link has failed, allowing the RPL link to be used for traffic. The other ring node adjacent to the RPL link, called the RPL neighbor node, may also participate in blocking or unblocking its end of the RPL link.
The event of an Ethernet ring failure results in protection switching of the service traffic. A Multicast automatic protection switching (APS) message is used to coordinate the activities of switching on/off the RPL link. Any failure along the ring triggers transmission of periodic APS messages (APS signal fail messages) along both directions from the ring nodes adjacent to the failed ring link after these ring nodes have blocked the ports facing the failed link. Upon reception of APS messages, the RPL owner node and the RPL neighbor node will unblock their RPL ports, creating yet another loop free ring topology. In this regard, a single link failure anywhere in the ring still ensures a loop free ring topology. After receiving the APS message, all ring nodes that receive the APS message in the Ethernet ring will flush their MAC addresses for the ring ports in their MAC table. In such instances, all data packets will be sent (flooded) by such ring node to both ring ports until the MAC addresses are re-learned for the MAC table.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.